/******************************************************************************
 * Spine Runtimes License Agreement
 * Last updated January 1, 2020. Replaces all prior versions.
 *
 * Copyright (c) 2013-2020, Esoteric Software LLC
 *
 * Integration of the Spine Runtimes into software or otherwise creating
 * derivative works of the Spine Runtimes is permitted under the terms and
 * conditions of Section 2 of the Spine Editor License Agreement:
 * http://esotericsoftware.com/spine-editor-license
 *
 * Otherwise, it is permitted to integrate the Spine Runtimes into software
 * or otherwise create derivative works of the Spine Runtimes (collectively,
 * "Products"), provided that each user of the Products must obtain their own
 * Spine Editor license and redistribution of the Products in any form must
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 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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 *****************************************************************************/

using System;

namespace Spine {
    /// <summary>
    /// <para>
    /// Stores the current pose for an IK constraint. An IK constraint adjusts the rotation of 1 or 2 constrained bones so the tip of
    /// the last bone is as close to the target bone as possible.</para>
    /// <para>
    /// See <a href="http://esotericsoftware.com/spine-ik-constraints">IK constraints</a> in the Spine User Guide.</para>
    /// </summary>
    public class IkConstraint : IUpdatable {
        internal IkConstraintData data;
        internal ExposedList<Bone> bones = new ExposedList<Bone>();
        internal Bone target;
        internal int bendDirection;
        internal bool compress, stretch;
        internal float mix = 1, softness;

        internal bool active;

        public IkConstraint(IkConstraintData data, Skeleton skeleton) {
            if (data == null)
                throw new ArgumentNullException("data", "data cannot be null.");
            if (skeleton == null)
                throw new ArgumentNullException("skeleton", "skeleton cannot be null.");
            this.data = data;
            mix = data.mix;
            softness = data.softness;
            bendDirection = data.bendDirection;
            compress = data.compress;
            stretch = data.stretch;

            bones = new ExposedList<Bone>(data.bones.Count);
            foreach (BoneData boneData in data.bones)
                bones.Add(skeleton.FindBone(boneData.name));
            target = skeleton.FindBone(data.target.name);
        }

        /// <summary>Copy constructor.</summary>
        public IkConstraint(IkConstraint constraint, Skeleton skeleton) {
            if (constraint == null)
                throw new ArgumentNullException("constraint cannot be null.");
            if (skeleton == null)
                throw new ArgumentNullException("skeleton cannot be null.");
            data = constraint.data;
            bones = new ExposedList<Bone>(constraint.Bones.Count);
            foreach (Bone bone in constraint.Bones)
                bones.Add(skeleton.Bones.Items[bone.data.index]);
            target = skeleton.Bones.Items[constraint.target.data.index];
            mix = constraint.mix;
            softness = constraint.softness;
            bendDirection = constraint.bendDirection;
            compress = constraint.compress;
            stretch = constraint.stretch;
        }

        /// <summary>Applies the constraint to the constrained bones.</summary>
        public void Apply() {
            Update();
        }

        public void Update() {
            Bone target = this.target;
            ExposedList<Bone> bones = this.bones;
            switch (bones.Count) {
                case 1:
                    Apply(bones.Items[0], target.worldX, target.worldY, compress, stretch, data.uniform, mix);
                    break;
                case 2:
                    Apply(bones.Items[0], bones.Items[1], target.worldX, target.worldY, bendDirection, stretch, softness, mix);
                    break;
            }
        }

        /// <summary>The bones that will be modified by this IK constraint.</summary>
        public ExposedList<Bone> Bones { get { return bones; } }

        /// <summary>The bone that is the IK target.</summary>
        public Bone Target { get { return target; } set { target = value; } }

        /// <summary>A percentage (0-1) that controls the mix between the constrained and unconstrained rotations.</summary>
        public float Mix { get { return mix; } set { mix = value; } }

        ///<summary>For two bone IK, the distance from the maximum reach of the bones that rotation will slow.</summary>
        public float Softness { get { return softness; } set { softness = value; } }

        /// <summary>Controls the bend direction of the IK bones, either 1 or -1.</summary>
        public int BendDirection { get { return bendDirection; } set { bendDirection = value; } }

        /// <summary>
        /// When true and only a single bone is being constrained, if the target is too close, the bone is scaled to reach it.</summary>
        public bool Compress { get { return compress; } set { compress = value; } }

        /// <summary>
        ///  When true, if the target is out of range, the parent bone is scaled to reach it. If more than one bone is being constrained
        ///  and the parent bone has local nonuniform scale, stretch is not applied.</summary>
        public bool Stretch { get { return stretch; } set { stretch = value; } }

        public bool Active { get { return active; } }

        /// <summary>The IK constraint's setup pose data.</summary>
        public IkConstraintData Data { get { return data; } }

        override public string ToString() {
            return data.name;
        }

        /// <summary>Applies 1 bone IK. The target is specified in the world coordinate system.</summary>
        static public void Apply(Bone bone, float targetX, float targetY, bool compress, bool stretch, bool uniform, float alpha) {
            if (!bone.appliedValid)
                bone.UpdateAppliedTransform();
            Bone p = bone.parent;

            float pa = p.a, pb = p.b, pc = p.c, pd = p.d;
            float rotationIK = -bone.ashearX - bone.arotation;
            float tx = 0, ty = 0;

            switch (bone.data.transformMode) {
                case TransformMode.OnlyTranslation:
                    tx = targetX - bone.worldX;
                    ty = targetY - bone.worldY;
                    break;
                case TransformMode.NoRotationOrReflection: {
                    float s = Math.Abs(pa * pd - pb * pc) / (pa * pa + pc * pc);
                    float sa = pa / bone.skeleton.ScaleX;
                    float sc = pc / bone.skeleton.ScaleY;
                    pb = -sc * s * bone.skeleton.ScaleX;
                    pd = sa * s * bone.skeleton.ScaleY;
                    rotationIK += (float)Math.Atan2(pc, pa) * MathUtils.RadDeg;
                    goto default; // Fall through.
                }
                default: {
                    float x = targetX - p.worldX, y = targetY - p.worldY;
                    float d = pa * pd - pb * pc;
                    tx = (x * pd - y * pb) / d - bone.ax;
                    ty = (y * pa - x * pc) / d - bone.ay;
                    break;
                }
            }

            rotationIK += (float)Math.Atan2(ty, tx) * MathUtils.RadDeg;
            if (bone.ascaleX < 0)
                rotationIK += 180;
            if (rotationIK > 180)
                rotationIK -= 360;
            else if (rotationIK < -180) //
                rotationIK += 360;

            float sx = bone.ascaleX, sy = bone.ascaleY;
            if (compress || stretch) {
                switch (bone.data.transformMode) {
                    case TransformMode.NoScale:
                        tx = targetX - bone.worldX;
                        ty = targetY - bone.worldY;
                        break;
                    case TransformMode.NoScaleOrReflection:
                        tx = targetX - bone.worldX;
                        ty = targetY - bone.worldY;
                        break;
                }
                float b = bone.data.length * sx, dd = (float)Math.Sqrt(tx * tx + ty * ty);
                if ((compress && dd < b) || (stretch && dd > b) && b > 0.0001f) {
                    float s = (dd / b - 1) * alpha + 1;
                    sx *= s;
                    if (uniform)
                        sy *= s;
                }
            }
            bone.UpdateWorldTransform(bone.ax, bone.ay, bone.arotation + rotationIK * alpha, sx, sy, bone.ashearX, bone.ashearY);
        }

        /// <summary>Applies 2 bone IK. The target is specified in the world coordinate system.</summary>
        /// <param name="child">A direct descendant of the parent bone.</param>
        static public void Apply(Bone parent, Bone child, float targetX, float targetY, int bendDir, bool stretch, float softness, float alpha) {
            if (alpha == 0) {
                child.UpdateWorldTransform();
                return;
            }
            if (!parent.appliedValid)
                parent.UpdateAppliedTransform();
            if (!child.appliedValid)
                child.UpdateAppliedTransform();
            float px = parent.ax, py = parent.ay, psx = parent.ascaleX, sx = psx, psy = parent.ascaleY, csx = child.ascaleX;
            int os1, os2, s2;
            if (psx < 0) {
                psx = -psx;
                os1 = 180;
                s2 = -1;
            } else {
                os1 = 0;
                s2 = 1;
            }
            if (psy < 0) {
                psy = -psy;
                s2 = -s2;
            }
            if (csx < 0) {
                csx = -csx;
                os2 = 180;
            } else
                os2 = 0;
            float cx = child.ax, cy, cwx, cwy, a = parent.a, b = parent.b, c = parent.c, d = parent.d;
            bool u = Math.Abs(psx - psy) <= 0.0001f;
            if (!u) {
                cy = 0;
                cwx = a * cx + parent.worldX;
                cwy = c * cx + parent.worldY;
            } else {
                cy = child.ay;
                cwx = a * cx + b * cy + parent.worldX;
                cwy = c * cx + d * cy + parent.worldY;
            }
            Bone pp = parent.parent;
            a = pp.a;
            b = pp.b;
            c = pp.c;
            d = pp.d;
            float id = 1 / (a * d - b * c), x = cwx - pp.worldX, y = cwy - pp.worldY;
            float dx = (x * d - y * b) * id - px, dy = (y * a - x * c) * id - py;
            float l1 = (float)Math.Sqrt(dx * dx + dy * dy), l2 = child.data.length * csx, a1, a2;
            if (l1 < 0.0001f) {
                Apply(parent, targetX, targetY, false, stretch, false, alpha);
                child.UpdateWorldTransform(cx, cy, 0, child.ascaleX, child.ascaleY, child.ashearX, child.ashearY);
                return;
            }
            x = targetX - pp.worldX;
            y = targetY - pp.worldY;
            float tx = (x * d - y * b) * id - px, ty = (y * a - x * c) * id - py;
            float dd = tx * tx + ty * ty;
            if (softness != 0) {
                softness *= psx * (csx + 1) / 2;
                float td = (float)Math.Sqrt(dd), sd = td - l1 - l2 * psx + softness;
                if (sd > 0) {
                    float p = Math.Min(1, sd / (softness * 2)) - 1;
                    p = (sd - softness * (1 - p * p)) / td;
                    tx -= p * tx;
                    ty -= p * ty;
                    dd = tx * tx + ty * ty;
                }
            }
            if (u) {
                l2 *= psx;
                float cos = (dd - l1 * l1 - l2 * l2) / (2 * l1 * l2);
                if (cos < -1)
                    cos = -1;
                else if (cos > 1) {
                    cos = 1;
                    if (stretch)
                        sx *= ((float)Math.Sqrt(dd) / (l1 + l2) - 1) * alpha + 1;
                }
                a2 = (float)Math.Acos(cos) * bendDir;
                a = l1 + l2 * cos;
                b = l2 * (float)Math.Sin(a2);
                a1 = (float)Math.Atan2(ty * a - tx * b, tx * a + ty * b);
            } else {
                a = psx * l2;
                b = psy * l2;
                float aa = a * a, bb = b * b, ta = (float)Math.Atan2(ty, tx);
                c = bb * l1 * l1 + aa * dd - aa * bb;
                float c1 = -2 * bb * l1, c2 = bb - aa;
                d = c1 * c1 - 4 * c2 * c;
                if (d >= 0) {
                    float q = (float)Math.Sqrt(d);
                    if (c1 < 0)
                        q = -q;
                    q = -(c1 + q) / 2;
                    float r0 = q / c2, r1 = c / q;
                    float r = Math.Abs(r0) < Math.Abs(r1) ? r0 : r1;
                    if (r * r <= dd) {
                        y = (float)Math.Sqrt(dd - r * r) * bendDir;
                        a1 = ta - (float)Math.Atan2(y, r);
                        a2 = (float)Math.Atan2(y / psy, (r - l1) / psx);
                        goto break_outer; // break outer;
                    }
                }
                float minAngle = MathUtils.PI, minX = l1 - a, minDist = minX * minX, minY = 0;
                float maxAngle = 0, maxX = l1 + a, maxDist = maxX * maxX, maxY = 0;
                c = -a * l1 / (aa - bb);
                if (c >= -1 && c <= 1) {
                    c = (float)Math.Acos(c);
                    x = a * (float)Math.Cos(c) + l1;
                    y = b * (float)Math.Sin(c);
                    d = x * x + y * y;
                    if (d < minDist) {
                        minAngle = c;
                        minDist = d;
                        minX = x;
                        minY = y;
                    }
                    if (d > maxDist) {
                        maxAngle = c;
                        maxDist = d;
                        maxX = x;
                        maxY = y;
                    }
                }
                if (dd <= (minDist + maxDist) / 2) {
                    a1 = ta - (float)Math.Atan2(minY * bendDir, minX);
                    a2 = minAngle * bendDir;
                } else {
                    a1 = ta - (float)Math.Atan2(maxY * bendDir, maxX);
                    a2 = maxAngle * bendDir;
                }
            }
            break_outer:
            float os = (float)Math.Atan2(cy, cx) * s2;
            float rotation = parent.arotation;
            a1 = (a1 - os) * MathUtils.RadDeg + os1 - rotation;
            if (a1 > 180)
                a1 -= 360;
            else if (a1 < -180)
                a1 += 360;
            parent.UpdateWorldTransform(px, py, rotation + a1 * alpha, sx, parent.ascaleY, 0, 0);
            rotation = child.arotation;
            a2 = ((a2 + os) * MathUtils.RadDeg - child.ashearX) * s2 + os2 - rotation;
            if (a2 > 180)
                a2 -= 360;
            else if (a2 < -180)
                a2 += 360;
            child.UpdateWorldTransform(cx, cy, rotation + a2 * alpha, child.ascaleX, child.ascaleY, child.ashearX, child.ashearY);
        }
    }
}
